1. Field of the Invention
This invention relates to technology for storing and reproducing information. More particularly, the invention relates to technology that can be effectively applied to a method of detecting defect in the information storage medium in the information storing/reproducing device, and to a defect detecting device.
2. Description of the Related Art
A general method of detecting defect will now be described with reference to a magnetic disk drive.
The magnetic disk drive stores and reproduces information into, and from, a storage medium for each of the sectors that are unit storage regions. FIG. 15 is a diagram illustrating a sector format. Each sector includes a PLO-SYNC 51 for drawing a PLL (phase locked loop) for synchronizing the clocks, a data-synchronizing signal 52 for obtaining a demodulation timing signal of a code modulated by detecting a DATA start position, a DATA portion 53 for really storing and reproducing data, and a CRC portion/ECC portion 54 for detecting and correcting defect. A GAP portion 55 which is a pattern for absorbing various kinds of delay times exists among the sectors.
A magnetic disk which is an information storage medium used for a magnetic disk drive contains the so-called defect region which is not suited for storing and reproducing information. The defect region occurs when the magnetic material for storing information is not uniformly spread on the storing surface in the step of production, when information is not stored due to dirt and scars on the storing surface, when signals for reproducing information are not produced to a sufficient degree or when large noise is superposed on the reproducing signals. Defect region could stem even from the so-called TA (thermal asperity) that occurs when the reproducing head comes into contact with the surface of the magnetic disk due to ruggedness formed by some reasons on the storing surface of the magnetic disk. The defect region usually maintains undesired properties and is not suited for storing information up to the future or for reproducing information. Therefore, the magnetic disk drive checks defect regions in advance, and registers the detected defect regions so that they will not to be used as data regions thereby to decrease defect in the information in the magnetic disk drive.
There has been proposed a method of detecting defect regions by taking the practical conditions of use into consideration. For example, Japanese Patent Laid-Open No. 145634/1997 discloses an defect detecting method by taking into consideration the defect correcting ability of a storing/reproducing device that is really used. Occurrence of error is detected by correcting error for each sector which is an information storage unit, and the defect in the sector is registered depending upon the number of error bytes corrected by correcting error.
This method makes it possible to omit the registration of small defects compared to error correction ability of the storing/reproducing device that is really used and, hence, to improve the yield of production by efficiently registering defect and to improve performance of the device by decreasing the frequency of substitute processing.
There has further been proposed a method of improving performance for detecting data synchronizing signals. According to, for example, Japanese Patent Laid-Open No. 216743/2001, performance for detecting data synchronizing signals is improved by utilizing, as part of the data synchronizing signal, the stored data of at least just before or just after the collated portion at the time when the data-synchronizing signal is detected during the reproduction. Namely, this method is to suppress defect at the time of reproducing information, and permits much defect. In detecting defect, it is important that a portion that may develop defect is reliably detected; i.e., portions that may develop defect are permitted to develop defect as much as possible so as to be detected. Therefore, permitting the occurrence of much defect is not suited for detecting defects.
The above method based upon the correction of error has a prerequisite in that the defect must be detected in a unit of sector and that the data must be correctly synchronized for properly correcting error. As for the DATA portion, CRC portion and ECC portion, defect can be detected as expected. However, error is not corrected for the portions where the data synchronizing signals are stored for synchronizing the data. Therefore, the data synchronizing signals are not capable of imparting a difference to the ability for correcting error between when defects are checked like in the data portion and when the data are really stored and reproduced using the device. This means that no margin is maintained to the data-synchronizing signal portion.
Further, a correct detection of the data-synchronizing signal is very important for demodulating the code of the subsequent DATA portion and, hence, a correct detection is always requested. That is, even when the data of which the code is demodulated in the DATA portion are flawless and have a very small error rate, a failure to detect the data-synchronizing signal which is usually about several bytes makes it difficult to correctly demodulate the code of the subsequent DATA portion of several tens to several hundreds of bytes. It is therefore desired that a defect in the data-synchronizing signal portion is detected as much as possible and is registered.
Further, in the device for storing and reproducing information by rotating a disk-like storage medium, such as a magnetic disk drive, a slight change occurs in the rotation of the storage medium. In really detecting defects and storing information as a device, therefore, the position where the data-synchronizing signal is stored differs every time when the information is rewritten. In detecting defect, therefore, defect does not exist in the data-synchronizing signal portion and is not detected. In subsequently storing information, the position for storing the data-synchronizing signal differs due to a change in the rotation of the storage medium resulting in an erroneous detection of the data-synchronizing signal and making it often difficult to reproduce the DATA portion that follows the data-synchronizing signal.
In order to correctly detect the data-synchronizing signal by taking the practical use into consideration, it is desired to maintain a margin to the defect in the data-synchronizing signal portion, to register the defect by detecting defect in the data-synchronizing signal portion as much as possible, and to detect the defect in the data-synchronizing signal by taking a change in the rotation of the storage medium into consideration, i.e., to precisely detect the defect at a position where the data-synchronizing signal is likely to be stored.
It is further desired to shorten the processing time for checking the defect.
Further, it is desired to improve reliability of the data-synchronizing signal or to decrease the region of the data-synchronizing signal portion by an amount that meets the improvement in the reliability of the data-synchronizing signal.
In the information storing/reproducing device, a reduction in the region of the data-synchronizing signal portion makes it possible to increase the region for storing/reproducing information, and to increase the storage capacity of information of the information storing/reproducing device owing to the improvement in the so-called format efficiency. Or, upon decreasing the region of the data-synchronizing signal portion and decreasing the information storing density per unit area in the information storage region, it is allowed to decrease error in the storage and reproduction and to improve performance of the information storing/reproducing device.